170 a spar doubler corrosion

[blueldr]

That hand screw extractor shown above for $25 at sears can be had from harbor freight for about $5. I've had one for years. Craftsman tools have a great warranty, but it isn't worth $20 on that tool.

[DaveF]

I once spent a pleasant week removing the fuel tanks from a Cherokee. Every screw was rusted in place. I found the slot method to be best, but one screw required drilling. I used a left-hand flute drill, which through a combination of torque and vibration backed the screw right out. I never had to use an extractor on it. Of course, you should always start with a shot of penetrating oil at least one day in advance.

[HA]

clean out the screw head so the driver bit fits tightly and full depth. use a good quality bit, either the Snap-on removal bits or other good quality. Use some valve grinding compound to keep it from slipping. and use a speed handle with a knob on the end which allows you to push down hard and gives you better leverage.

at least the day before, use Kroil or Mouse Milk on all the screws.

things like stuck screws can really drive up the labor bill on annuals etc and many owners (you guys excepted of course) don't understand how much time it can take. I fired a mechanic once who when reinstalling panels would cam out all the screws with his drill driver and then laughed about it, "It would stink to be the guy that has to take these out!"

[cpolsley]

I removed my tanks about 18 years ago to inspect for corrosion. All the screws on the front spar portion of the tank cover came out with no problems. The screws on the wing tip and aft end of the tank panel were the more difficult ones to get out. You can see these screws through the wing inspection panel. I used a rivet gun and the screw driver like attachment on a very low setting. Some screws it helped others it didn't and I ended up rendering many of the screw slots unusable.

I was able to just grab the screw head on a few with a pair of vise grips and got a few more out. At least two or three I ended up drilling the head to the point I was able to chip off the head with the tap of a chissel. These screws I later removed by using vise grips, clamping to the threaded end of the screw and twisting the screw as if tightning it until it threads all the way through so as not to damage the nut plate threads.

After you have disconnected both rubbers hoses from the outlet and vent line, as well as removing the sump drain be very careful you don't bend or damage the two outline extensions coming out of the tank. These are 2" to 3" in length and must clear that rib before you lift the outer end of the tank up. I became impatient and bent my vent line so bad it ripped a very small opening in the tank where its welded on. I had to take the tank to a shop and have it repaired. I used an angle grinder with the roll lock scotch brite pads and cleaned the entire cavity. I painted the tank compartment with zinc chromate, spray can. If I had it to do over again, which I probably should, I would brush on the Dupont Vari Prime, there would be no overspray issues and it would probably be a better overall coating.

With the tank removed it would be a good time to replace or rebuild your fuel gauges, I have read how-to topics on that in other areas of the forum. In addition to replacing the gasket at the filler neck I found the tank restraining straps needed the anti-chaf material replaced as well. Remember the screws are structural so be sure you get the correct part number screws. Give yourself plenty of time for the project, in my case a day was not enough.

[FredMa]

If anyone is planning on doing an inspection of their spars as mentioned here I would recommend using a corrosion inhibiting compound on the hardware during reassembly to prevent the hardware issues diescribed here. There are several products that can be used. My favorite is Cor-Ban 27L. It comes in a small squeeze tube similar to the small rtv tubes you are familiar with. Mastinox in also commonly used in commercial aviation but is very carcinogenic.

[FredMa]

How's the repair coming along, or has it started yet? I have an extra tube of Cor-Ban 27L for the screw when you put it back together if you like.